Atomic-Scale Variations of Interfacial Water Structure Driven by Site-Specific Chemistry

Although
interfacial solution structure impacts environmental, biological and
technological phenomena, including colloidal stability, protein assembly,
heterogeneous nucleation, and water desalination, its molecular details remain
poorly understood. Here, we visualize the three-dimensional (3D) hydration
structure at the boehmite(010)-water interface using fast force mapping (FFM). Using
a self-consistent scheme to decouple long-range tip-sample interactions from
short-range solvation forces, we obtain the solution structure with lattice
resolution. The results are benchmarked against molecular dynamics simulations
that explicitly include the effects of the tip with different levels of approximation
and systematically account for tip size, chemistry, and confinement effects. We
find four laterally structured water layers within one nanometer of the surface,
with the highest water densities at sites adjacent to hydroxyl groups. The
findings reveal a complex relationship between site-specific chemistry, water
density, and long-range particle interactions; and represent a major step
forward towards quantitative data interpretation and widespread implementation
of 3D FFM.